The present invention relates to a battery condition detecting apparatus to correctly grasp conditions of a battery, i.e., capacities thereof, and also a charge control apparatus for an automobile, for setting a charge target value of a battery based on conditions of the battery mounted on the automobile with employment of the battery condition detecting apparatus, and for charging the battery at this target value during the drive operation.
As shown in JP-A-53-127646, as a conventional means for detecting capacities of a battery mounted on a vehicle, with the capacity of the battery obtained from the discharge characteristic while the starter is started, the charge/discharge currents of the battery after this capacity are accumulated, or multiplied.
Thus, when the battery capacity detecting means detects that the capacity of the battery is lowered, it is possible to prevent the battery from being lowered by cutting out a predetermined electric load from the battery. Also, there has been proposed such a method for controlling power generated by the alternator, taking account of the capacities of the battery and the conditions of the vehicle.
In general, a battery has a charge characteristic as represented in FIG. 5. That is to say, as indicated by a solid line of this figure, an increase ratio of a capacity to a charge current (referred to as a "charge efficiency") is substantially 100% under such a condition that the capacity of the battery is lower than about 80% of the actual capacity when this battery is a new product. However, if the capacity of the battery becomes higher than about 80% of the actual capacity by being charged, since gassing (such a phenomenon that while the battery is charged and the capacity thereof is increased, the voltage of the electrode is increased; and when this electrode voltage is increased higher than a predetermined value, water contained in the battery fluid is subjected to electrodialysis due to the charge current) may happen to occur, the charge efficiency is gradually lowered. Then, while the battery is deteriorated, a timing at which the gassing phenomenon commences is gradually shortened, namely a timing at which the charge efficiency starts to be lowered is gradually shortened, and also the charge efficiency is rapidly lowered. The capacity at which the battery can be charged (referred to as "a maximum capacity") is reduced and then the capacity cannot be increased to the actual capacity (=maximum capacity of a new battery). In other words, there are differences in the charge characteristics of a new battery and a deteriorated battery. A dot line shown in FIG. 5 indicates one example of the charge characteristic for the deteriorated battery.
Furthermore, a capacity of a battery is also reduced due to a discharge operation. As a consequence, according to the conventional battery condition detecting method, even when lowering the battery capacity may be detected, no detection is made that this detection is caused by either the discharge operation, or the battery deterioration.
Then, to control power generated by the alternator taking account of the conditions of the vehicle, it is absolutely necessary to charge the battery. In case when the battery is deteriorated, most of the charge currents are used for the gassing, so that the battery fluid is reduced, which may cause adverse influences to the lifetime of the battery. There is another problem that although the capacity of the battery is not increased under such a condition that the maximum capacity is lowered and the charge current is continuously supplied to the battery, if the charge operation is continued, lowering the battery fluid caused by the gassing is further increased.